1. Field of the Invention
This invention relates to mechanical mountings for interchangeable lenses, and more particularly to a changeover device for effecting operation in the manual exposure mode and the automatic exposure mode.
2. Description of the Prior Art
It is known to provide a lens barrel having a construction wherein when the lens is attached to and tightened in the camera, the signal member in the lens mounting is maintained in non-rotative relation relative to the control member in the camera body, and wherein a manual-and-automatic exposure mode changeover device is used as disclosed in U.S. Pat. No. 3,864,707 of Shirasaki.
The coupling mechanism of the Shirasaki patent is constructed in the form of a tightening ring constrained at the rear end portion of the lens barrel and axially movably fitted thereon, while the tightening effect is produced by the bayonet member provided in the tightening ring. The interchangeable lens assembly with such coupling device is, however, difficult to handle during attachment to and detachment from the camera body.
A new type of mechanical mounting has been proposed which is improved over the Shirasaki patent with respect to the manageability of the coupling device and which retains the feature that the signal member in the lens assembly is maintained responsive to the camera mechanism in a predetermined position so that the signal communication can be accurately established. This mechanical mounting comprises an adapter member restrained from rotation in a predetermined position relative to the camera body during mounting, and lens barrel means including a main support tube rotatable relative to the adapter member and a bayonet carrying member. In the disassembled condition, before the lens assembly is attached to the camera body, the adapter member and lens barrel means are maintained in predetermined relationship to each other, and the signal member for transmission of exposure information is also maintained in predetermined constant position along with the adapter member. When the lens assembly is attached to the camera body, the operator may grasp any part of the lens barrel means, such as the focusing ring, or the diaphragm presetting ring fitted on the main support tube, and by turning the lens barrel means about the optical axis, coupling between the bayonet member of the lens assembly and the bayonet member of the camera body may be effected.
The structure of the mechanical mounting for the lens employing this new coupling mechanism is complicated, and it is particularly difficult to incorporate an exposure mode changeover device for transmitting a selected one of the signals representative of the manual exposure mode and the automatic exposure mode in the mechanical mounting of this construction wherein the adapter member carrying the signal member is fixed relative to the camera body while the lens barrel means is rotated during mounting.
The arrangement of a changeover pin for transmission of the selected signal in a predetermined position of the camera through the adapter member involves particular difficulty with regard to accurately controlling the relative spatial relationship between the individual members since the diaphragm setting ring is caused to rotate when the lens is attached.